Cellular communication networks are nearly ubiquitous, providing reliable two-way voice communications. More recently, cellular communication networks are being used to provide data communications as well.
Reliably sending data over a wireless communication network presents technical challenges because of the very nature of data transmission. By its very nature, data (as opposed to voice signals and digitized representations of voice) is typically generated and sent intermittently, characteristically sent in bursts or packets. Reliably transmitting bursts of high-speed data through a communications network requires that a path exist through the network to avoid data loss.
In a wireless CDMA communications system, an encoded data packet is transmitted by a CDMA radio every twenty milliseconds. These digitally encoded signals broadcast from a mobile radio are usually received by more than one cell site base station receiver. The data packets that are picked up at the cell sites that hear the signal from the mobile radio are routed to circuits known as channel elements within the cell site equipment. Cell sites that hear the CDMA mobile forward the received data packets from the channel elements to other circuits known as frame selectors via a switching network linking the cell sites to the frame selector circuits centrally located in a selector distribution unit or SDU. In many instances, the switching network linking cell sites to a selector distribution unit is an asynchronous transfer mode (ATM) switching system.
Frame selector units in the SDUs evaluate the several different CDMA samples received from the cell sites and select a particular CDMA sample of those xe2x80x9cheardxe2x80x9d by the various cell sites based upon a determination of which sample has the best (most error-free) data. Every twenty milliseconds the CDMA samples from a mobile unit are re-evaluated so that the best data signal is used to reconstruct the original signal.
The frame selector units and especially the channel elements are relatively scarce resources in a typical wireless system. For a voice call, a channel element at a cell site is allocated to the mobile call for the duration of that call on that cell. Likewise for the frame selector in the SDU and the transmission path between the allocated channel element and frame selector. For a data call however, more than one channel element at a cell site may be assigned to the mobile data call when it is necessary to transfer a burst of data. It is advantageous to share the channel elements at a cell site among several mobile data calls that intermittently have bursts of data to transfer but are otherwise not transferring data. This sharing of channel elements necessitates the establishment of different communication paths between the set of channel elements at cell sites and the set of frame selectors at one or more SDUs.
A problem with sending high-speed data through a CDMA communications system is that the path between the channel elements and the frame selectors through a switching network always requires a finite amount of time to set up. Bursts of high-speed data can be lost or, the service quality level can deteriorate because of the time required to set up a path through a switching network.
Lost data packets can be catastrophic to data message integrity. A CDMA wireless communication system that prevents burst data losses would be an improvement over the prior art. A CDMA wireless communication system that is able to quickly establish needed communication paths can provide improved service over the prior art.
New functionality provided to CDMA cell sites and CDMA SDUs reduces call set up time and improves high-speed data handling through a CDMA network. This new functionality is provided by way of computers and computer programs that establish and maintain communication links through a switching network linking the cell sites to the SDUs. These computers and computer programs include virtual end point processors in both the cell site and SDU that together establish one or more communication paths through the switching network. Signaling manager computers and software coordinate the creation and maintenance of logical communication paths. Call manager computer and/or software is responsible for coordination of activities relative to each call. Such a call manager is commonly embodied in a base station controller.
In the preferred embodiment, the CDMA cell site virtual end point processor is controlled by the cell site signaling manager, to establish and maintain a communication link through an ATM switching network linking the cell site to an SDU. The cell site virtual end point processor communicates through the ATM network with a virtual end point processor within the CDMA SDU that is under the direction and control of an SDU signaling manager. When an actual call must be routed from the cell site to the SDU, the call manager communicates with the cell site signaling manager. The cell site signaling manager dynamically assigns channel elements and couples data signals from a CDMA mobile radio seeking communication privileges to that CDMA cell site channel element. The cell site signaling manager arranges with its counterpart in the SDU to couple the frame selector for the radio channel to the previously established ATM network communication path, and then couples the CDMA channel element to the previously-established ATM network communication path via the cell site virtual end point processor. The SDU signaling manager couples the allocated frame selector to the previously established ATM network communication path.